1. Field of the Invention
The present invention relates to a numerical control apparatus that controls a machine tool, and specifically, relates to a numerical control apparatus to reduce a path length to a start point in a canned cycle.
2. Description of the Related Art
A numerical control apparatus performs, upon one instruction, machining a workpiece from a material shape of the workpiece to a finishing shape thereof in accordance with a canned cycle constituted of a plurality of cutting cycles for each cutting cycle of which a movement path from a start position of the movement path to an end position thereof is formed of a plurality of paths as one cutting cycle which conventionally causes a return once from a cutting completion position in the cycle to a start position of the cycle or a movement along only a first planar axis to start the next cycle. Herein, the first planar axis designates an X-axis in the case of an XY-plane, designates a Z-axis in the case of a ZX-plane and designates a Y-axis in the case of a YZ-plane. Moreover, a second planar axis designates the Y-axis in the case of the XY-plane, designates the X-axis in the case of the ZX-plane and designates the Z-axis in the case of the YZ-plane.
As to the conventional canned cycle, a region for which a workpiece has been already cut is not determined but the above-mentioned operation is always performed for preventing interference with the workpiece. As a solution against this problem, section “Solution” in Japanese Patent Laid-Open No. 10-293606 discloses the followings as a method for configuring the path. A cutting state determination unit is provided to detect spindle load exerted on a tool in executing a specific cutting block of a machining program to determine an actual cutting state of the workpiece with the tool. A tool position detection unit is provided to detect the position of the tool when it is determined that the cutting state is changed. A program rewriting unit is provided to rewrite, as a target section of a rapid traverse instruction G0, a section in which the tool does not actually cut the workpiece in the specific cutting block, of the machining program, instructed with a rewriting instruction mark on the basis of a determination signal of the cutting state from the cutting state determination unit and a tool position in the occasion of the change in cutting state detected by the tool position detection unit.
Moreover, as another solution, section. “Solution” in Japanese Patent Laid-Open No. 2008-9758 discloses a method of performing predetermined machining by moving the tool relatively to the workpiece on the basis of a stored machining program, a program storage unit storing the machining program in which a cutting feed instruction for instruction of a cutting feed from a cutting feed start position and a rapid traverse instruction for instruction of rapid traverse to the cutting feed start position are described. According to the method, a contact detection unit is provided to monitor the presence or absence of contact of the tool with the workpiece. On the basis of a detection signal from the contact detection unit, the cutting feed start position of the machining program is changed to change and set the movement path of the tool to the cutting feed start position in the rapid traverse instruction.
However, the cutting control apparatus disclosed in Japanese Patent Laid-Open No. 10-293606 above does not reduce the path but changes the section which is not actually in the cutting state for the cutting block to the rapid traverse one to reduce cycle time. Hence, cycle time cannot be reduced when rapid traverse blocks are originally set, this being a problem.
Moreover, the machine tool disclosed in Japanese Patent Laid-Open No. 2008-9758 above changes the movement path for a path corresponding to a rapid traverse instruction regarding one block. Hence, paths of rapid traverse instructions regarding a plurality of blocks cannot be reduced, the reduced path is a cutting block, and the contact detection unit as hardware is necessary, these being problems.